1. Field of the Invention
The present invention relates to a rotational angle detecting apparatus and a torque detecting apparatus comprising one or a plurality of targets provided at a rotor and a plurality of detecting means, disposed opposite to the targets, for outputting detection signals having phases different from each other in accordance with each position of the targets as the rotor rotates.
2. Description of Related Art
Known as one of steering apparatuses for an automobile is an electric power steering apparatus capable of reducing driver's load by driving an electric motor to assist steering. Such an electric power steering apparatus comprises an input shaft joined to a steering wheel, an output shaft connected to steerable wheels by a pinion and a rack or the like and a connection shaft for connecting the input shaft with the output shaft so as to detect, by a torque sensor, a steering torque applied to the input shaft on the basis of a torsional angle generated at the connection shaft and to drive an electric motor for steering assist, which interlocks with the output shaft, in a controlled manner on the basis of the steering torque detected by the torque sensor.
The present applicant has suggested in Japanese Patent Application No. 2002-69121 a rotational angle detecting apparatus comprising one or a plurality of first targets provided at a rotor; first detecting means, disposed opposite to the first targets, for outputting a detection signal as the rotor rotates; second detecting means for outputting a detection signal having a phase different from that of the detection signal outputted from the first detecting means; second targets, provided at a rotor, the number of which is coprime with the number of the first targets; third detecting means, disposed opposite to the second targets, for outputting a detection signal as the rotor rotates; and fourth detecting means for outputting a detection signal having a phase different from that of the detection signal outputted from the third detecting means, wherein a rotational angle of the rotor is detected on the basis of the detection signals respectively outputted from the first detecting means, second detecting means, third detecting means and fourth detecting means. The application also suggests a torque detecting apparatus (torque sensor) comprising this rotational angle detecting apparatus and a steering apparatus comprising this torque detecting apparatus.
According to the conventional rotational angle detecting apparatus and torque detecting apparatus, since a detection signal outputted from one detecting means includes curved portions in the vicinity of the relative maximum value and the relative minimum value, two detecting means for outputting detection signals having phases different from each other are provided so as to obtain a linear detection signal by switching between the two detection signals in order to detect the angle and the torque. Such a structure, however, may do harm to steering feeling since discontinuous portions form in the detected angle signal and torque signal and in the differential signals thereof.